Spin-phonon coupling in van der Waals antiferromagnet VOCl

We report magnetization and Raman spectroscopy study on single crystals of VOCl, a van der Waals antiferromagnetic material. Magnetization measurement confirms an antiferromagnetic transition at 79 K and a magnetic easy axis along crystallographic a direction. The temperature-dependent Raman spectrum reveals five peaks at 30 K. Below the Neel temperature T_N, the Raman-active modes 247 cm^-1 and 404 cm^-1 remarkably deviate from the standard Boltzmann function, which is ascribed to the strong magnetoelastic coupling between spins and phonons. We further observe an anomaly in 383 cm^-1 mode at around 150 K. This coincides with the broad maximum in VOCl's magnetic susceptibility, suggesting a development of short-ranged magnetic order at this temperature.